Formation of appropriate synaptic connections during early development create the structural basis for the complexities of brain function. Ionic currents play roles in growth cone selection of a neuronal targeted for innervation and establishment of neurotransmission that is important for synaptic stabilization. An ideal CNS pathway in which to study synaptic targeting and stabilization is found in the auditory system, whereby cochlear nucleus bushy cells innervate, via the largest nerve terminal in the brain called the calyx of Held, experimental opportunities to probe electrical ionic and cell-cell signaling events in single calyces and their targets during synaptogenesis, which are little understood in neural system. In Aim 1, we will determine the role of calcium signaling in mediating the initial stages of growth cone-target contact, using calcium signaling in mediating the initial stages of growth cone-target contact, using calcium sensitive dyes along with standard and confocal fluorescence imaging. Aim 2 will resolve the onset of synaptic transmission in the calyx and its role in synapse stabilization and maturation of postsynaptic ionic currents. Whole-cell recording from MNTB neurons will be used to monitor spontaneous postsynaptic currents and assay the maturation of ionic conductances prior to and following the time of contact by calyceal axons. In Aim 3 we will identify the protein constituents of a specialized adherens complex found in calyx terminals and its developmental sequence in relation to the early stages of synapse formation and stabilization. This project builds on our observations that this structure is located adjacent to synapses and may contain elements involved in topographic patterning of neural connections. This project is innovative because it provides a CNS model for studying pre- and postsynaptic events underlying early synaptogenesis and builds on our observations of a unique adherens organelle in the calyx of Held. These results will be significant because they will contribute knowledge essential to studies of biochemical and molecular events that underlie synapse stabilization.